Temperature control of exothermic reactions



Nov. 15, 1932. A. BOND TEMPERATURE CONTROL OF EXO'I'HE RHIG REACTIORS 8 Filed April 2; 1930 INVEN 0R. Ma 4', BY

A TTORNE ya.

Patented Nov. 15, 1932 UNITED sTATEs PATENT oF1=1c 1 EABLAN A. BOND, OF METUCHEN, NEW JERSEY, ASSIGNOR, BY EIESNE ASSIGNMENTS I TO THE ROESSLER & HASSLACHER CHEMICAL COMPANY, OF NEW YORK, N. Y

CORPORATION OF DELAWARE TEMPERATURE con'rnor. or xornmmo REACTIONS Application filed April 2, 1930. Serial no. 441,013.

plied to gas phase exothermic reactions con ducted in the presence of solid, porous, heat conducting catalyst bodies.- Such reactions occur in the oxidation. of organic compounds and frequently in other types of reactions. If the temperature is not properly regulated side reactions occur, the products decompose and/or the initial materials pass through thereaction zone unreacted.

The invention will now be more particularly described in reference to the oxidation of methanol vapor by air in contact with such catalysts as silver. v

Theoretically, the reaction should proceed 1 according to the following equation CH OH+2y volumes air 0 +2N CH O H 2N This reaction is highly exothermic. Temperature regulation is essential for several reasons. If the temperature is too high, the catalyst body may be fused or sintered or be otherwise in ured so that it no longer functions properly. High temperatures also promote the decomposition of the formaldehyde which results in undesirable by-products such as carbon monoxide and hydrogen or may even cause deposition of carbon on the catalyst.

On the other hand, the reaction proceeds slowly, if at all, at very low temperature, under which conditions, the reaction is not selfsustaining and requires the application of ex-' ternal heat, or the reaction ceases to give maximum yields because a considerable portion of the methanol is not oxidized and appears. in

the final roduct. An obJect .of the present invention is to facilitate the control of temperature in the oxidation of methanol to formaldehyde and similar exothermic reactions and thereby increase yields. 1

It has been found that the specific reaction .above proceeds favorably with catalysts such as silver in various forms between temperatures of about 400 to 850 (3., and preferably the reaction temperature is maintained around 500 to 750 C. Y I

Although the reaction is highly exothermic, it does not begin at low temperatures although at higher temperatures the exothermic heat makes it self-sustaining. It is therefore necessary to start the reaction'by applying heat to the reactants. Thismay be done in any convenient fashion either by directly heating the reaction chamber from-the outside, or by preheating the catalystby hot gases through the reaction cham til the necessary starting temperature haspassing er unbeen reached. After the reaction begins, it, if properly controlled, should be self-sustain ing and it will under these conditions develop more heat than is desirable. The problem then becomes one of heat removal.

Prior methods of heat removal have u'tilized the method of abstracting heat throu h the walls of the reaction chamber at rig t angles to the direction of. the flow of the gaseous reactants.

Such a method of heat extraction is unsatisfactory, becauselarge temthat whereas the temperature of the reaction zone. near the walls of the reaction chamber in such a system may be around'300", the temperature within or near the center of the reaction zone, which is remote from the point of heat extraction, may be 700 or 800 or even higher. This leads to very inefficient conditions because the reactants passing through the cool catalyst near the periphery of the reaction zone will notbe converted to formaldehyde,- whereas those near the center are overheated and decomposition results. The yields, therefore, suffer both because methanol is found in the final product and because a portion of the formaldehyde which .has been formed is decomposed. This condition' also causes sintering of the catalyst in the hot zone, which results in non-uniform trol is, of course, applicable to any thermally alyst mass due to a change in the resistance to the flow. Moreover, the sintered catalyst, because of its decreasedsurface, is, even if penetrable, comparatively inactive.

gradually and uniformly decreasing the tem.

pprature from plane to plane in the direction 0 viding a system such that all points in any given plane of cross section through the zone of heat production, perpendicular to'the directlon of gas flow, are equidistant from and in excellent thermal connection with acooled surface of uniform temperature through whlch the heat is conducted'away. In other gordsf the straight line paths of thermal ow producing zone, to, the cooling medium-{are equal in length and thermal cOnductivityQ T rom all points on any plane in thejheat Preferably t e entire path of heat outflow extends through a material of excellent ther-f mal conducting properties.

eat is extracted. This method ofheat conducting catalyst, and is of particular value fthe catalystmass has a high thermal conductivity. It has been found -thattli'i's' can be satisfactorily accomplished, "for example, when employing a catalystfof liigh', thermal conductivity such as electroly'tic 'fs v er crystals, obtained by electrical "idepo'si. tion from acid solutions.- ,Th'eseflc ys alf massesare reduced to a s'ize about emanates. I and looselypacked in the reaction chamber. There they are supported on a metal surface throughwhich heat is abstracted. 'As "ex-5;? amples of other satisfactory catalyst'material...

the following may be mentioned porous sil verobtained by pilling and reducing silver' oxide'or other silver. compounds and other commonly noted forms of porous silver;

lb 1 is a vertical section of anapparatus suita le for carrying out the process of the invention. v Fig. 2 is a plan view, partially. in section of the apparatus shown in Fig. 1.

base plate forms the exit end of the reaction chamber and the catalyst 5 rests in thermal It has now been found that the temperature may be regulated uniformly and at will by gas flow. This" is accomplished by pro- 1 cat'al ace crystals tdjadeptli contacttherewith. This base is perforated with aseries. of holes 6 through which the reaction products are led into the conduits 7 and thence tov a header 8 from which they are taken for further treatment. If the holes drilled in thebase are large in diameter as compared with the catalyst particles a metallic wire screen such as silver wire gauge of suitable mesh may be placed between the catalystand the base. Numerous small holes in the base will serve as well.

' Thisbaseplate is then immersed to any desired depth in a coolingmedium, such as Water, contained in the tank 11; the amount of heat removed by the cooling medium will depend upon the depth to which the base is submerged, as well as upon the temperature of the cooling medium. The bottom of this base plate is preferably cut into rid es and grooves 10,, leaving an increased sur ace exposed to facilitate controlled heat transfer tQQthe,eoolinggmedium.

I The double walls 15 and 3, of the reaction .ifchamber-ienclose an insulating material 4: so all" the heat removal takes sent P a t r ng he coolin'g'maybe'efiected by any suitable heatofl izat-ion provide efiicient point of contact'with the catalyst, one near the center and "one near the edge. The temperatureat the top of the catalyst ranged v froni 595to 605;G.,-during the run, whereas Referring to the accompanying drawing:

the theoreticaltemperaturedeveloped by this reaction without cooling would be about 1000 C. The temperature at the base of the catalyst body was maintained at 250 to 260 .Jbas plateexcept for that remov edfas -.sens1ble heat of the exit gases.

-n eans, for; example, by immersin the base pl'ateincooled running water or y perinit- 'tingfthewatertoboih'inwhichcase the latent The catalyst, where the essential heat .de-j velopment' occurs, should therefore,- be H a p v ood thermal contact with the surface wh" invention will further xam'plerwith reference ,1; into the :metien s'f downward through the m'p ed ;ojf electrolytic silver v v bout'% inch. The gas rate through the catalyst'was at a space velocity of 5 0,0Q0-per hour ,(N, T. P.) The gases essary strength, resistance to the corrosive action of the reaction products and which does not catalyze the reaction in an undesirable fashion can be used.

It will further be noted that by suitably regulating the temperature of the catalyst support on the one hand and the thickness of the catalyst bed on the other handboth the temperature of the hottest plane in the cata- 1 st and the average temperature throughout the catalyst may be varied as desired.

A wide variation in the type of apparatus, size of reaction chamber and process with which said apparatus is employed is also possible. For example, the direction of gas flow might be reversed. The major portion of heat would then be removed at the entrance of the reaction chamber. The top as well as the bottom of the chamber might contact with the catalyst and heat be removed from both ends. So long as the walls are insulated a zone of uniform temperature perpendicular to the gas flow will be maintained and the method of heat removal is fundamentally the same. The catalyst employed will vary from process to process. They are generally suitable to this process if porous to the gas flow and possessing thermal conducting properties. It will'therefore be understood that the invention is not to be limited to the particular apparatus and process described, but that all processes and apparatus wherein tem rature is controlled in the manner here-- in escribed come within the scope of this invention.

I claim: v

1. A method of regulating the temperature of exothermic gas phase reactions wherein the gases to be reacted are passed through a permeable heat conductin catalyst body, which comprises removing heat from the reaction zone along straight line paths of thermal flow in the direction of the gas flow within the catalyst chamber while reventing removal of heat from such cham r in-a direction transverse to the as flow.

2. A method of regulating the temperature of exothermic gas phase reactions wherein the gases-to be reacted are passed through a permeable heat conducting catalyst bod which comprises removing heat uniform y through and from lane's perpendicular to the gas flow in t e reaction zone by uniformly cooling the exit end of said catalyst body throughout its whole extent while preventing removal of heat from the reaction zone in a direction transverse to the gas flow.

Signed at Perth Amboy in the county of Middlesex and State of New Jersey this 31st day of March, A. D. 1930.

' HARLAN A. BOND. 

